1. Field of the Invention
The present invention relates to a semiconductor formed of a polycrystal silicon thin film, which is formed by crystallizing an amorphous silicon thin film on an insulator, and a thin-film transistor using that semiconductor.
2. Description of the Related Art
In recent years, a technique has been popularly researched where an amorphous silicon thin film is formed on an insulator such as a quartz substrate, allowed to grow into a solid-phase crystal (SPC) through a heating treatment or an annealing process due to the irradiation of a laser beam or an intense light to form a polycrystal silicon thin film.
A conventional general technique for obtaining a polycrystal silicon thin-film by allowing an amorphous silicon thin film to grow in a solid phase will be described below.
First, an amorphous silicon thin film having a thickness of 500 to 5000 Å is formed on a quartz substrate.
Thereafter, the amorphous silicon thin film thus formed is heated to 400 to 1100° C. and subjected to an annealing process to make the amorphous silicon thin film grow into crystal. In this situation, a heater, infrared rays or the like is used as heating means.
The annealing process may be conducted by the irradiation of a laser beam or an intense light other than heating.
In the above-mentioned manner, a polycrystal silicon thin film is obtained.
The polycrystal silicon thin film thus obtained is used as an active silicon layer of the thin-film transistor (TFT), to thereby provide a thin-film transistor. As a result, a liquid-crystal display unit, image sensor or the like which is high in operation speed and in image quality is obtained using the above thin film transistor.
Up to now, the polycrystal silicon thin film obtained by annealing the amorphous silicon thin film has difficulty in lowering a defect density in crystal.
The thin-film transistor using the polycrystal silicon thin film thus formed as the active silicon film is hindered from realizing an improvement in various characteristics of the thin-film transistor, for example, the lowering of a threshold voltage (Vth), an increase in mobility, a decrease in a leak current (Ioff), etc., because the defect density in the active silicon layer is high.